Is there such a thing as mental illness? Or are we simply less tolerant of departures from the "normal" than our ancestors were?
For one example, were chronically depressed people just accepted as sad people, whereas now there is the idea that we have some kind of right to be happy, and even cheerful?
Obsessive/compulsive people could basically be laughed at? Sure they would be difficult people to be married to, but that was true of a lot of people.
And of course: some of the "mentally ill" were considered to be inspired directly by God or the devil, or some other kind of divinity or spirit. This could mean veneration--or instant death.
h/t grand rounds/Dr. Val's Better Health.